(1) Field of the Invention
This invention relates to new methods of photolithographic fabrication of alignment posts and optical interference layers directly on liquid-crystal-on-silicon displays.
(2) Description of the Prior Art
The picture quality of liquid crystal displays that are created using as simple a design as seven segments to complex designs using millions of pixels is determined by the structure that is used to control the variation of the height of the pixels and the location of the external wires after wafer processing has been completed. There are known processes for creating insulating alignment posts based on preformed glass micro-spheres and rods; relatively low series resistance posts can be obtained by means of selective deposition of polysilicon and metallic silicide. (The making of metallic vias and contacts is a comparatively well known processing art.)
U.S. Pat. No. 5,498,925 to Bell et al describes the formation of posts in flat panel displays using processes based on a heat-treated slurry or paste upon a glass plate. U.S. Pat. No. 5,597,736 teaches the function of a light-blocking layer deposited upon a semiconductor substrate material that can emit light. U.S. Pat. Nos. 5,744,824 and 5,748,828 show various LCD structures and external optics.
Until now, it has been difficult to construct alignment posts using photolithography and also add optical interference layers simultaneously onto a semiconductor substrate material used to control the gray-level of each pixel.
A principal object of the present invention is to describe various new methods for building a flat-panel liquid-crystal display upon an integrated circuit (IC) die with inter-related alignment between the posts supporting the overlaying glass cover plate and optical interference layers employed to improve image quality.
Another object of this invention is to describe effective and very manufacturable methods of photolithographic formation of insulating alignment posts (also called studs or pillars). These methods can be used in processing many different device types, and are described in this application for liquid crystal display devices as a way of illustrating their embodiment at a pixel density beyond that achievable with preformed micro-glass spheres and rods.
A further object of the present invention is to describe methods of deposition for both the posts and the optical interference layers that are independent of each other and retain their desired feature during deposition of subsequent features. The various methods are classified into five method categories: 1) silicon oxide wet etching; 2) amorphous silicon plasma etching; and 3) nitride plug filling; 4) insulating material lift-off; 5) photosensitive polyimides.
Five new methods for the formation of an improved liquid-crystal-on-silicon display are described, in which the device structure is enhanced by the photolithographic building of alignment posts among the mirror pixels of the micro-display. At the same time these five methods accommodate the fabrication of an optical interference multilayer that improves the image quality of the reflected light. These five methods are:
Silicon Dioxide Posts by Wet Etchingxe2x80x94wherein said alignment posts are formed by the process of silicon dioxide wet etching upon the said silicon substrate.
Amorphous Silicon Posts by Plasma Etchingxe2x80x94wherein said alignment posts are formed by the process of amorphous silicon plasma etching upon the said silicon substrate.
Silicon Nitride Posts by Plug Fillingxe2x80x94wherein said alignment posts are formed by the process of silicon nitride plug filling upon the silicon substrate.
Insulation Material Posts by Lift-Offxe2x80x94wherein said alignment posts are formed by the process of insulation material lift-off upon the said optical interference layer OIL.
Polyimide Posts by Photosensitive Etchingxe2x80x94wherein said alignment posts are formed by the process of polyimide photosensitive etching upon the OIL.